RD&D-Programme 2004 - SKB

13.2.4 Backfill
Together with Posiva, SKB is studying a number of different concepts for tunnel backfilling.
This, along with tests of different clay-based materials, continues to be a prioritized activity,
see section 18.1.6. The long-term evolution of the backfill shares several issues with the buffer,
and the same type of knowledge is required, although scope and relative importance may differ.
Processes that are still of importance to investigate are swelling, the subsequent long-term
mechanical evolution, section 18.2.9, and factors that can affect it, including chemical action,
section 18.2.13, and colloid formation and erosion, section 18.2.17.
13.2.5 Geosphere
The development of models for rock movements continues, with a focus on upcoming safety
assessments, most immediately SR-Can. Model development is described in section 19.2.7.
One question in particular that is being investigated in this context is postglacial faulting.
Models for groundwater flow are being developed, principally to obtain numerical models for
calculations for the safety assessment. Further knowledge of groundwater flow has been gained
from the supraregional simulations that have recently been carried out for Northern Uppland
and Eastern Småland. From now on, special attention will be devoted to surface hydrology.
Model development for groundwater flow is described in section 19.2.3.
A number of activities are under way aimed at gaining greater knowledge of the transport
resistance and how it can be used to calculate the transport of radionuclides dissolved in the
groundwater. The transport resistance retards this transport and is an important property of the
rock. Processes that still need to be investigated include advection/mixing, section 19.2.12,
diffusion in the rock matrix, section 19.2.14, colloids, section 19.2.20 and 19.2.21, and
modelling of radionuclide transport, section 19.2.26.
Hydrogeochemical conditions are always investigated on the site. The task of the research
programme is to supplement the geochemical investigations, shed light on the stability of
prevailing conditions, and attempt to predict the changes that can occur, in the short term as a
result of the fact that the repository is kept open, and in the long term due to the influence of
foreign substances, see section 19.2.19. Processes that need to be studied are reactions with the
rock, section 19.2.15, dissolution and precipitation of fracture-filling minerals, section 19.2.16,
and microbial processes, section 19.2.18.
13.2.6 Biosphere
Describing the biosphere and its evolution is an important part of the safety assessment, since
it is in the biosphere that any releases from the deep repository would have consequences.
The biosphere is being thoroughly characterized in conjunction with the site investigations.
Furthermore, it is necessary to predict what changes might occur in the future and what importance
they might have for possible releases. The greatest attention will be devoted to the first
1,000 years. The subsequent period up until the next ice age can be dealt with in less detail.
In order to calculate the transport of radionuclides in the biosphere it is necessary to know the
release points. In other words, a more coherent description is needed of hydrogeological and
oceanographic processes all the way up to the release points, see section 20.5. Transport in
the biosphere is described with compartment models where the biosphere is divided into units
between which the transfer of radionuclides is calculated, see section 20.4.
Continued work will be devoted to further defining and describing the most important processes
in different types of ecosystems, such as terrestrial, section 20.6, and aquatic, section
20.7. Long-term variations in climate, land uplift and salinity can have a great impact on the
150 RD&D-Programme 2004